fix(updater): don't fail AppImage installs when the temp dir is another mount of the same file system (#3688)

* fix(updater): skip a backup location the AppImage cannot be renamed into

Two mounts of one file system share st_dev, so install_appimage could
pick a bind-mounted or private temp dir and then fail every install with
EXDEV. Move on to the next location instead; the last one is the
AppImage's own directory.

* Apply suggestion from @lucasfernog

---------

Co-authored-by: Lucas Fernandes Nogueira <lucas@tauri.app>

.changes/updater-appimage-cross-mount.md

@@ -0,0 +1,6 @@
+---
+updater: patch
+updater-js: patch
+---
+
+On Linux, installing an AppImage update no longer fails with `Invalid cross-device link (os error 18)` when the temp or cache directory is a separate mount of the AppImage's file system, such as a bind-mounted or private `/tmp`. The backup now moves on to the next location, ending with the AppImage's own directory.

plugins/updater/src/updater.rs

@@ -1234,7 +1234,11 @@ impl Update {
                     let permissions = std::fs::metadata(&self.extract_path)?.permissions();
 
                     // create a backup of our current app image
-                    std::fs::rename(&self.extract_path, tmp_app_image)?;
+                    match std::fs::rename(&self.extract_path, tmp_app_image) {
+                        Ok(()) => {}
+                        Err(err) if err.kind() == std::io::ErrorKind::CrossesDevices => continue,
+                        Err(err) => return Err(err.into()),
+                    }
 
                     #[cfg(feature = "zip")]
                     if infer::archive::is_gz(bytes) {